1. Field
The present invention relates to an apparatus for switching multiple electrical inputs to multiple electrical outputs. More particularly, the present invention relates to a broadband RF micro electromechanical system (MEMS) switch matrix that can be scaled to a matrix size of M×N, where M comprises the number of RF input ports and N comprises the number of RF output ports.
2. Description of Related Art
The routing of RF signals may be accomplished by using a switching matrix. A switching matrix may be configured to map M signal input ports into N signal output ports. Switching matrices are found in many signal routing situations such as communications base-stations, switched beam antennas, or telecommunications transfer switches. FIG. 1 shows a typical application of a switch matrix 100 that is used to switch signals from and to satellite processing circuits 101, satellite up-links 102 and satellite downlinks 103.
Various methods and devices are known in the art for providing switch matrices that allow M inputs to be switched to N outputs. U.S. Pat. No. 4,399,439, issued Aug. 16, 1983 to L. C. Upadhyayula, describes an M by N switch matrix comprising M single pole input switches, each input switch having N throws, connected to N single pole output switches, each output switch having M throws. A total of M times N interconnects are required to connect the input switches to the output switches. Upadhyayula further discloses that the input and output switches may be fabricated from GaAs MESFET transistors to provide for switches useful at microwave frequencies. However, those skilled in the art would understand that scaling the Upadhyayula apparatus to a larger number of inputs and/or outputs would increase the size and complexity of the individual input and output switches and the size and complexity of the apparatus overall.
M by N switch matrices may be provided by multiple crossbar switches. U.S. Pat. No. 5,696,470, issued Dec. 9, 1997 to R. M. Gupta et al. discloses techniques for using multiple crossbar switches to accomplish 2×2 and 4×4 matrices. Gupta et al. further describe a solid-state electronic switching module capable of operating at microwave frequencies for providing for switching of signals at those frequencies. However, one skilled in the art would appreciate that scaling the devices disclosed by Gupta et al. to larger matrices would require increasing levels of integration or the provision of several discrete devices, which also increases the overall size and complexity of the switching matrix. Another crossbar switch capable of operating at microwave frequencies is disclosed in U.S. Pat. No. 5,309,006, issued May 3, 1994 to Willems et al. Switch matrices using the Willems et al. device would suffer from the same limitations discussed above for the Gupta et al. device.
Another well-known technique used for providing M×N switch matrices is through the use of a crosspoint switch matrix. FIG. 2 shows a schematic representation of a 4×4 crosspoint switch matrix 200. In the crosspoint switch depicted in FIG. 2, each RF input 201, 202, 203, 204 is connected to a corresponding row transmission line 211, 212, 213, 214. Each RF output 221, 222, 223, 224 is connected to a corresponding column transmission line 231, 232, 233, 234. Each row transmission line 211, 212, 213, 214 crosses each column transmission line 231, 232, 233, 234 at crosspoints 240. Connections across the crosspoints 240 and from the row transmission lines 211, 212, 213, 214 to the column transmission lines 231, 232, 233, 234 are provided by crosspoint switches 241, 242, 243. With the crosspoint switch matrix 200 depicted in FIG. 2, any of the RF inputs 201, 202, 203, 204 may be connected to any of the RF outputs 221, 222, 223, 224 by opening or closing the appropriate crosspoint switches 241, 242, 243. For example, to connect RFIN1 to RFOUT3, the crosspoint row transmission line switches 241 at points A and B are closed, the crosspoint column transmission line switches 242 at points D, E and F are closed, and the crosspoint switch 243 at point C is closed.
Crosspoint switch matrices have been fabricated using semiconductor devices. U.S. Pat. No. 5,446,424, issued Aug. 29, 1995 to J. A. Pierro, discloses a crosspoint switching matrix employing multilayer stripline and pin diode switching elements. Pierro discloses a multiple layer structure in which one layer contains row transmission lines and a separate layer contains column transmission lines. Pin diode arrays are placed in apertures within the structure to provide crosspoint switching among and between the row and column transmission lines. One skilled in the art will appreciate that the fabrication of the device according to Pierro may be quite complex, due to the need to fabricate the multiple layers and to insert the pin diode arrays at each crosspoint. Also, scaling the device according Pierro to a large number of signal inputs and/or outputs may also be difficult, due to the need to fabricate all of the row or column transmission lines within a single layer.
Therefore, there exists a need in the art for an apparatus and method that provides for switching multiple electrical inputs to multiple electrical outputs in a low cost and scalable fashion. Further, the apparatus and method should provide low insertion loss for the radio frequency signals to be switched and to provide high isolation between separate radio frequency signals over a broad bandwidth.